Add structural OpenAPI schema to Tekton CRDs

[siamaksade]

Kubernetes 1.15 introduced structural OpenAPI schema which helps with validation, supporting kubectl explain and also building tools around it:

Structural schema should be added for all CRDs introduced by Tekton.

[siamaksade]

This PR is related: #1179

[imjasonh]

Is this something that can be easily generated using existing tooling? I'm a bit worried we'll end up with structs and YAML validation out of sync, and I'm also a bit uncomfortable with maintaining code to generate one from the other. Is there something OpenAPI provides for this?

[vdemeester]

/kind feature
/kind question

[tekton-robot]

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[tekton-robot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.
If this issue is safe to close now please do so with /close.

/lifecycle stale

Send feedback to tektoncd/plumbing.

[tekton-robot]

Rotten issues close after 30d of inactivity.
Reopen the issue with /reopen.
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/close

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[tekton-robot]

@tekton-robot: Closing this issue.

In response to this:

Rotten issues close after 30d of inactivity.
Reopen the issue with /reopen.
Mark the issue as fresh with /remove-lifecycle rotten.

/close

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